Home HVAC question - is it worth it to...?

Brief overview: 2 story house, level 1 is 1/2 underground. Forced hot air and cent. air - uses the same vent system designed for heat only.

The lower level is generally cool and damp while the upstairs is hot and drier. I was thinking of hooking up an independent vent system to pull air from one level and bring it to the other. Hopefully based on the temp difference between the 2 levels.

My questions are:
1 is this worth doing?
2 should I try to use the existing vent system to do this?
3 Hi Opal!
4 is there a thermostat that operates on temp dif. (instead of direct temp) that is available at ‘consumer’ prices?
5 which direction should the air be pulled from (1st/2nd level)
5 anything else I should know about this?

This is what works for me. In the Summer I block off the vents in the lower level, and leave only the upstairs to be cooled. The lower level naturally stays cooler, and the cold air from upstairs will make its way downstairs.
In the winter I block off the vents to the upper level, and let the air rise from the lower level to heat the upstairs since heat rises naturally the upstairs needs less heat to keep it warm.
Doing this will probably raise your electic bill a little due to the fact that you are blocking off some of the system.
The best and much more expensive way to take care of the problem is to have 2 hvac systems. One for the lower, and one for the upper.

I have use the block the lower vent trick in the summer and bolck the upper vents trick in the winter. The seal on the vents isn’t perfect so some air gets through which is fine.

ripping out a 1 yr old central a/c and furnace to install dual zones is not an option.

in the winter it’s not a big deal but in the summer the lower level gets so humid. The a/c would remove humidity but most of the vents are closed.

perhaps I could do something with the intake vent like draw more from the lower level by closing up the intake vent. This might risk freesing the coils though

Our main duct coming from the HVAC splits in two, part going to the main floor and part going upstairs. We can adjust it right at that point, so there’s no wasted energy going to blocked-off vents.

You might examine your ductwork to see what you have; you wouldn’t have to rip out the heating or cooling units, just get the ducts changed.

Also, no matter what kind of system you have, a ceiling fan is helpful. You set it to blow upward in summer and downward in winter.

The simplest solution would be to install a de-humidifier in the lower level.

Another option: Modify your cold air return system. A cheap and efficient way to help cool the house. We have a similar set up on a Tri-level (garden, main, upstairs). We have two cold air returns one on the main level and one upstairs. The cold air returns are floor level, are 32 inches wide and had a fixed grate. If your system utilizes the wall itself, you can install a louvered grate at floor level and cut out a Hot Air return at ceiling level directly above the cool air return. Install a louvered grate at ceiling level also. In the winter, close the louvers on the Hot Air return and have the Cool Air open. In the summer when you are running the AC, close the floor level Cool Air return and open the Hot Air return.

this is how it’s set up here but cutting down the air flow either in intake or vent will risk freezing the coils but it’s worth a shot.

I do have a dehumidifier but would rather not use it since it’s noisy and the a/c is a dehumidifier and would like to make better use of it.
** Sn-man** that might be the ticket, as i said the system was designed for only heat and latter retrofitted for the a/c - installing ceiling level intakes might work out good or at least better - can I just use a open wall cavity (sheetrock and 2x4) box for this intake or do I have to run a duct?

also where is the best place to put the intake - the cold damp air downstairs or the hot dry air upstairs

Wow - are you that drifter that took up residence in my downstairs? :smiley: Seriously though, I have the exact same problem, and my temperature stratification is unbelieveable - I have a delta T of 15 degrees or more from the downstairs den to the upstairs bedroom - 15 degrees!

Since I have a side-to-side split, I plan on making a vent, with a small fan, to continuously circulate air - either drawing it up from the lowest level to the top, or reversing it. I know a person here who has done the same thing, and has sworn to me that, on his side-to-side split, it felt like he got a “whole new furnace/AC”, it worked so well.

  1. This will depend on a lot of factors, but IMO yes.
  2. If you can. My friend used a custom vent made from 4-inch PVC pipe, with a reversible fan mounted in the top end. He was able to run the pipe down through the walls vertically by starting in the attic - he was damn lucky he could, too.
  3. Hi Opal too.
  4. I haven’t seen one, but you could make one. Hey, I know, it’s not the best way but it’s not that hard either.
  5. This is a tough one. I guess it would depend on where the vent ducted to. In the Summer, I think I would want cold air drawn up to the bedrooms - although it would be humid. But then again, if you draw hot air down, then the AC maybe has time to dehumidify some of it as it drifts back up the three stair levels through the house…this might be a GD topic almost. :slight_smile:

Whatever you do, you simply must tell us how it works.

use what the hvac people call CAC, constant air circulation. on your thermostat, if you have air, you will notice the fan switch has two positions, auto and on. flick the switch to “on.” this will keep your furnace fan (but not the furnace) running all the time, night and day all day. this will help stabilize the temperature in your home as well as the humidity. just make sure you replace your filters as often as needed.

wouldn’t that be a hoot - what time I’d save not having to type so many things on this board - just go upstairs and ask.

I’m glad to see I’m not the only one who was thinking of this and someone actually did this and it worked - a very good sign. Also standard drywall/stud construction has a gap of 3.5" how did your friend use 4" pcv?

THe easiest way to run such a system would be throught the garage so I would have to insulate the ducts which I don’t think it’s that big a deal.

As for CAC - we sometimes run the fan on continously but my wife doesn’t like this setting because of the vents blow where she normally wants to be. Also the intake is on one side of the downstairs ( the upstairs is about 1/4 over to one side and 3/4 to the other) so even with the CAC the rooms furthest away from the intakes don’t seem to mix well - that’s where I was thinking of installing the extra venting system.

You can just use the wall cavity. It made a pretty big difference for us.

I asked - he didn’t use 4 inch PVC, but he can’t remember what it was. I mis-remembered the size.

It still works well, according to him.